1. Field of the Invention
The present invention relates to an oil-cooled piston for an internal combustion engine. More particularly, the invention relates to a piston having an annular plate covering an annular cooling oil duct in the piston head.
2. The Prior Art
Pistons are known from German patent Nos. DD 252 638 Al and DE 41 34 530 Al, in which an annular plate in the form of an open sheet metal ring covers the cooling oil duct. These rings are supported either in a groove on the inside of the ring belt or the outside of the central annular rib of the piston. The rings are subjected to elastic deformation according to the Seeger ring principle; that is, they are initially stressed in the radial direction.
However, the rings according to these references cannot be used with pistons having a large piston pin diameter and correspondingly large piston pin bosses. With large piston pin diameters, installation of the annular plate is problematic to an extent that the annular plate cannot be used at all or can only be used to partially cover the cooling oil space.
A cooled piston with a separate head and skirt is known from German patent No. DE 40 39 752 Al having an annular hollow space in the piston head for receiving cooling oil. The lower part of the annular hollow space is sealed by a sheet metal ring that may consist of two separate parts. The inner periphery of the sheet metal ring is provided with a collar which rests against the rib of the piston head. The outer periphery of the sheet metal ring rests on the piston skirt which flexes the sheet metal ring upward and is then coupled to the piston head by the piston pin bushings. A disadvantage of this design is that the sheet metal ring is supported by both the piston head and the piston skirt.
German patent No. DE 36 43 039 Al discloses a sheet metal ring divided into two halves for sealing the lower portion of an annular cooling oil space in the piston head of a multi-part cooled piston. The sheet metal ring is fastened to the piston head by a flanged collar that extends from the inner surface of the ring belt. The sheet metal ring can also be attached by welding, soldering or screwing the sheet metal ring to the ring belt. This design presents numerous disadvantages in that it is expensive to manufacture and additional fastening elements are required to attach the sheet metal ring to the piston head.